Process for producing alkyl aluminum compounds



United States Patent 3,505,375 PROCESS FOR PRODUCING ALKYL ALUMINUMCOMPOUNDS Marcelian F. Gautreaux and Andrew 0. Wikman, Baton Rouge, La.,assignors to Ethyl Corporation, New York, N.Y., a corporation ofVirginia No Drawing. Filed Nov. 1, 1966, Ser. No. 591,133 Int. Cl. C07f/06 US. Cl. 260448 10 Claims ABSTRACT OF THE DISCLOSURE The manufactureof alkyl aluminum compounds involving the reaction of aluminum andhydrogen is catalyzed with a complex, partially alkyl, species oftitanium, zirconium, or niobium. A typical catalyst precursor is atitanium, zirconium or niobium alkoxide; particularly a lower alkoxide,such as titanium tetraisopropoxide.

This invention relates to the preparation of alkyl compounds of aluminumand in particular to the preparation of such compounds by the directprocess from hydrogen, aluminum and ethylene employing catalyticmaterials.

The direct reaction of aluminum with hydrogen and olefin to producetrialkylaluminum compounds is disclosed by Horace E. Redman in US.Patent 2,787,626 issued Apr. 2, 1957. As a result of this teaching andothers related to it the manufacture of trialkylaluminum compounds hasbecome a large-scale commercial operation. In such reaction, theactivation of aluminum appears to be an important consideration.Numerous variations relating to the activation of aluminum in this typereaction as well as in others have been set forth, typical of thesebeing activation with sodium materials in the United States patents ofHerbert B. Fernald, 3,077,490 and 3,100,786, issued Feb. 12, 1963 andAug. 13, 1963, respectively. Other patents in this area include the US.patents to Elmer H. Dobratz, 2,892,738; 2,908,562 and 3,026,345 issuedJune 30, 1959, Oct. 13, 1959 and Mar. 20, 1962, respectively.

Another activation arrangement for aluminum is disclosed by Frederick J.Radd and Warren W. Woods in US. Patent 3,104,252 which issued Sept. 17,1963, in which the aluminum reactant is in the form of an alloycontaining an added reaction promoting amount of one or more of severalcatalytic elements, titanium, zirconium, hafnium, vanadium, niobium,scandium, and uranium. This activation involves certain metals which aresaid to form peritectic binary systems with aluminum and mentions that,of 51 metallic elements tested in aluminum alloys for the purposes ofthe invention, only the seven noted above have been found to work asactivators. Aside from general discussions along the line indicated, thepatent does not develop much theory as to mechanism however it isbelieved that the titanium alters the crystal structure of aluminum andmakes it more capable of reaction with hydrogen.

Another line of patents relating to the activation of aluminum involvehalogens as shown in the patent to Ziegler which issued in the Republicof South Africa as No. 263/55 and the patent to Dow which issued inBelgium as 548,652.

Another prior art patent in this general area, US. 2,271,956 toRuthruff, indicates that the reaction of olefin, aluminum, and hydrogenin the presence of an aluminum halide yields dialkylaluminum halide andmonoalkylaluminum dihalides. Associating this teaching with theteachings of Zieglers South African patent and noting the discussion asto activation of aluminum in the various teachings, it is withconsiderable interest that one notes that 3,505,375 Patented Apr. 7,1970 the elements which are considered to be inhibitors or poisons forthe reaction in US. Patent 3,104,252 are considered to be activators ofaluminum for the reaction of 2,271,956.

Together the foregoing patents deal with the so-called activation ofaluminum by the elements and inorganic and organic compounds of thealkali metals and alkaline earth metal classes (IA and II-A), as well asheels of organoaluminum compounds. Additionally elements of the scandiumand titanium classes (IIIB and IVB) are mentioned as activators as arethe halogens (VIII-A). Certain classes of transition metals arediscussed as both activators of aluminum and reaction inhibitors. Othermaterials, such as silicon are also discussed as both inhibitors andactivators. As an example for silicon US. 3,104,252 discusses one sideand French Patent 1,409,564 discusses the other. To this last group asfar as inhibitors are concerned perhaps can be added oxygen and oxygencontaining materials because of the tendency of oxygen to form aninactive A1 0 film that supposedly is removed in the early describedZiegler ball-mill technique. Also carbon and nitrogen probably tend tosuppress the reaction by dilution without solution. (Note that theclasses referred to above are those as set forth in the 1955 PeriodicChart of the Fisher Scientific Company.)

All of the foregoing activator materials except the heel arecontaminants as far as a high purity trialkyl aluminum product isconcerned. Of more serious consequences, some of these materials (suchas sodium) form active compounds or complexes with aluminum and some ofthem such as titanium form highly active catalysts for certain reactionssuch as ethylene polymerization that are undesired in certain instanceswhere the product trialkylaluminum compounds are used, as for example asa basic building block for controlled chain growth with ethylene. Thus,aside from the expense involved, one seeks to hold to a minimum theamount of additive used. In many instances this is a difficultproposition because it is not generally possible to determine much inadvance how a particular combination of reactant lots will behave. Thusone must usually specify an operating procedure or materials which willreact under the most adverse conditions. Reaction will be obtained butuniformity of product is still missing. Particularly is this true withthe titaniumalloy of US. Patent 3,104,252 because alloys are notoriousfor variable properties and any additive thereto must be inserted far inadvance of the reaction and cannot be conveniently changed after theformulation of the alloy. Thus it is not unusual that titaniumquantities vastly greater than the -500 parts per million quantityseemingly adequate in accordance With US. Patent 3,104,252 are usuallyused by proponents of the alloy system.

In view of the state of the art with regard to the activation ofaluminum in the preparation of alkyl aluminum compounds, it issurprising that an entirely new technique for enhancing the productionof alkyl aluminum compounds has been discovered which providessubstantial improvement with a comparative simplicity of the overallprocess. The present technique may be employed to advantage as the soleintentional improvement for this type of reaction yet on the other handit may be combined to advantage with various forms of activationreviously known intentional or otherwise such as those discussed in theforegoing. The improvement of the resent invention preferably usesorgano compounds of titanium and related materials as catalysts. Thesecatalysts can be added to the reactants or to the reaction mass itselfon an individual-batch or instantaneous-concentration basis which can bemanipulated at will so as to maintain a high degree of uniformity inreaction rate with minimum contamination of the product. Catalysts canbe added directly or generated in situ from precursor materials. Theefiectiveness of the titanium and related materials used as catalystshere appears to be vastly greater than that of titanium and likematerials used in alloys as aluminum activators. The present techniqueis particularly advantageous in cooperation with the sodium activationand heel techniques discussed in the foregoing, it appearing that thesedifferent activation techniques plus the catalysis may influencediiferent ones of many sequential reactions involved in the overallprocess, the actual activation of aluminum possibly being only one ofseveral such sequential reactions, with the catalytic factor influencingthe rate controlling reaction.

Likewise the present catalysis teachings can be used in combination withresidual titanium class materials in the aluminum in the sense thatprior removal of all traces of such from the aluminum is not necessary.In many instances, however, one does not wish to have routinely presenta high content of titanium class materials because of carry-over to thetrialkyl aluminum product and prefers to pay extra for higher purityaluminum and use the teachings of the present invention which permitsvariation of amount of organo titanium and related materials even frombatch to batch for precise control and greater uniformity of reactionand product.

The constituents of the class identified as titanium and relatedmaterial include the members of Groups III-B, IV-B and V-B of thePeriodic Table (Fisher Scientific Company, 1955). In general, organotitanium and to a lesser extent organo zirconium materials are preferredcatalysts on a cost-effectiveness basis. Organo niobium materials areuseful but less preferred. Specific compounds particularly desirable areorgano materials such as alkoxides having comparatively small numbers ofcarbon atoms per organo radical because of their desirable physicalcharacteristics particularly as regards stability, availability, boilingoint and melting point, and because of their greater percentage ofactive metal bonds available on a weight basis. Since alkyls of titaniumand many related materials are not particularly stable and are not easyto produce and isolate, a preferred form which possesses desiredcharacteristics for the purposes of the present invention includes thealkoxides, particularly those of the lower organo groups such as thosehaving from about 26 carbon atoms per organo radical. Uniform materialssuch as titanium isopropoxide and alkyl-alkoxide combinations of variousratios can be used as well as mixtures involving radicals with up toabout 20 carbon atoms per organo radical. Another basis for describingthe catalyst which is desirable in some instances is to use compounds inwhich the carbon chains of the organo radicals correspond to the desiredproduct alkyls, simplifying purification operations. Thus titaniumexthoxide (tetraethoxy-titanium) and ethyl triethoxy titanium may beused in preparing triethyl-aluminum. Titanium isopropoxide has excellentcatalytic characteristics in connection with the production of the loweralkyl aluminum compounds, such as triethylaluminum andtriisobutylaluminum, particularly in the direct reaction of olefin,aluminum and hydrogen combined with sodium activation and the use of aheel from a previous run, the latter activations being used as taught inthe prior art. Using such technique it is generally possible to obtainexcellent results in the production of triethylaluminum usingcomparatively small quantities of titanium tetraisopropoxide such asabout 0.01 to 5.0 percent by weight of catalyst fed relative to aluminumfed. A more preferred catalyst proportion is from about 0.04 to about2.0 percent by weight with from about 0.05 to about 1.0 most preferred.These ratios are on the basis of a particular compound (tetraisopropoxytitanium) and therefore depend to some extent upon the particular formand size of alkyl radicals involved. Other materials will normally beused in ratios :giving equivalent mols of metal alkoxide fed per gramatom of aluminum fed. In general, the broad ranges include the workableand desirable ranges which are preferred because they fall between onelimit of excessive catalyst for purchase cost and separation expenseconsiderations and the other limit of negligible eifectiveness.

To illustrate the magnitude of the improvement readily obtainable whenutilizing the teachings of the present invention, comparative data showan increase in reaction rate by a factor of a proximately 25 whentitanium alkoxide is added to a poorly reactive aluminum systern whenused on the basis of about 0.8 wt. percent of tetraisopropoxy titaniumrelative to aluminum in the reactants fed. The reason for the greateffectiveness of the catalysts is not known however certain theoriesseem plausible. Surprisingly, one cannot achieve results such as thoseof the present invention by adding titanium powder or titanium hydrideto the reaction mass. Even titanium dioxide is not as effective as thepresent systems. This seemingly eliminates the possibility thatelemental titanium or titanium metal per se is a catalystor isconvertible into a catalytic species by reactions in thealuminumhydrogen-olefin system. The fact that titanium hydride does notshow results seemingly rules out its participation as a catalyst incorresponding metal hydride reactions with olefin which parallels theAlH type of reaction to form titanium alkyls. Literature informationalso appears to bear this out by emphasizing the unstable nature oftitanium alkyls leading one to suspect that they might not be formed inthe first place. Titanium dioxide seems to be rather insoluble.

It is believed that a fundamental or rate limiting step in the reactionof aluminum, hydrogen and olefin is a reaction of aluminum and hydrogento produce some form of aluminum hydride species according to a reactionsuch as: (A) 2Al+3H AlH This involves a five body collision of materialsin different phases (solid hase and liquid phase) which has a lowprobability.

Where the principles of the present invention are used, it is believedthat a far simpler tri-molecular type of reaction occurs (as shown fortitanium materials):

In this instance the collisions of reactants are much simpler and thehydrogen and titanium alkoxide are more closely related to a solutioncondition so that the reaction can occur. The variable valence oftitanium is also beleived to be a contributing factor in its change fromthe n to the n1 state, It usually being 4.

Probably this is a simplification as to the species of titanium materialthat is the effective catalyst and also in that catalyst regeneration isnot shown however, once the possibility of such is established, it isquite evident that here we can have a catalytic system in comparison toa mere aluminum activation system which seeks to make the aluminum moresusceptible to reaction in the S-body collision type of reaction.

Various possibilities in reaction such as (B) above can be consideredparticularly as regards the eifective catalytic species and the variouspossible exchanges in which it can become involved.

In the first place it is believed likely that the effective catalyticspecies is a complex partially alkyl species such as:

R MZ where M is titanium, zirconium or niobium, or mixtures thereof.

R is hydrocarbon alkyl, aryl, alkaryl, arakyl, cycloalkyl and the likeand may conatin compatible substituents. R is preferably lower alkyl upto about 6 carbon atoms.

x+y is a valence factor which is 4 where M is titanium and zirconium and3 where M is niobium; x can be zero or positive, but not negative.

Z is O'R, where R is as R above plus Ti and Al, which are moieties oftitanium and aluminum respectively, a moiety representing merely apartial molecular structure where is shown only one bond of a titaniumor aluminum atom involved at that point. Such a configuration normallyis related to a bridging or association of two M atoms via the Olinkage. R and R can be similar or different and where y is greater than1, the Zs can be similar or different.

The foregoing effective catalysts can be supplied to the system in suchform or can be generated in situ from precursor materials, particularlyM alkoxides, such as lower titanium alkoxides; for example, tetraethoxytitaniurn, tetraisopropoxy titanium, tetrabutoxy titanium and the like.A precursor material that is frequently particularly desirable becauseof the ease and low cost of producing it as above and comparative easeof handling is tetraisopropoxy titanium.

Where such a precursor material is supplied to an AlR reaction systemsuch as a triethylaluminum system or a triisobutylaluminum system, afirst probable reaction (shown for typical tetraalkoxy titanium) is theinsitu generation of the effective catalyst R TiZ according to thereaction:

The involvement of R TiZ in the reaction with aluminum and hydrogen maycome about through an R exchange or a Z exchange or both. The R exchangeis simpler and is discussed first with the aid of the following reactionsequence:

In Equation 1 the catalyst R TiZ is reduced to a lower valence statewhich in turn goes to a further lower valence state in a second step ofEquation 2. In each of Equations 1 and 2 aluminum alkyl dihydride isformed as a short lived intermediate which is soluble and hence readilyreactive with soluble olefin in a bi-molecular fashion according toEquation 3 to produce R Al without further necessity for involvement ofthe catalyst. The catalyst is regenerated in Equation 4 with hydrogenand olefin, however, a similar regeneration may occur in the presence ofhydrogen and a heel of AlR through a splitting-off of alkyl residues.

A similar series of reactions occurs with the Z exchange however thereis greater complication at this point because of a greater number ofalternate reaction possibilities due in part to concurrent R and Zexchanges.

From the above it is observed that sequential reactions are shown inwhich the five-body collision requirement of the aluminum-hydrogenreaction is avoided and solubilities are comparatively favorable. It isbelieved that to avoid making erroneous generalizations it is desirableto point out that certain titanium salts particularly TiCL; are known tohave desirable effect in olefin polymerization and in the displacementof hydrocarbon residues from aluminum through a process of splitting offthe original hydrocarbon residues as olefins and the attachment of thenew olefins in their place as different bydrocarbon residues. Both ofthese known processes can be placed in the same category by regardingthem as the addition of an olefin to an aluminum-hydrogen bond(displacement) or to an aluminum-hydrocarbon bond (polymerization).These are of the nature of reactions (3) and (3') above. The presentcatalyst systems are believed to operate with regard to the differentreactions of (1), (1'), (2), (2), (2"), (2"') above, which are notinvolved in polymerization and displacement.

In the following examples, two grades of aluminum were employed forcomparative purposes. The first grade (for Examples 1 and 2) was ofcomparatively high purity in th range of 99.7-99.9 percent aluminum.Other impurities were quite small and a sample was selected as typicalmaterial of low titanium and silicon content (less than 50 parts permillion) so as to avoid any alloy activation thereby. The reactionproceeded well in noncatalyzed Example 1 but significantly better whencatalyst was added in Example 2.

For Example 3, etc., a lower grade of aluminum was chosen as a typicalinexpensive production grade which had given poor results in previousexperimentation. This material was fairly low in iron contamination butwithout any outstanding content of any particular contaminant,particularly titanium and silicon.

EXAMPLE 1 A mixture of 73 g. of triethylaluminum, 35 g. of finelydividedaluminum powder, and 0.3 g. of sodium was heated to C. in a 250-ml.turbine-agitated Magne- Drive autoclave under 1000 p.s.i.g. hydrogenpressure. Hydrogen to maintain the pressure constant at 1000 p.s.i.g.was fed continuously to the autoclave from a 250-ml. feed reservoirmaintained at a higher pressure. The pressure drop in the feed reservoirwas plotted as a function of time and the maximum slope of this line wastaken as a measure of the relative reaction rate, which varies with thereactivity of the aluminum powder employed. A slope equivalent to 200p.s.i.g. pressure drop in 35 minutes is arbitrarily assigned a relativereactivity of 1.00. In this example, the relative reactivity was foundto be 0.79. This method of experimentation was selected because it isrepresentative of the rate determining aluminum plus hydrogen reactionand minimizes indeterminate variables such as hydrogenation of olefin.Results are comparable in general when olefins are used for the completese quence.

EXAMPLE 2 Example 1 was repeated, using the same grade of aluminumpowder, with the addition of 0.25 g. of titanium isopropoxide. Therelative reactivity was 2.23.

EXAMPLE 3 Example 1 was repeated, using a different grade of aluminumpowder. The relative reactivity was 0.20. This same grade of aluminumpowder was used in Examples 4l0.

EXAMPLE 4 Example 3 was repeated, with the addition of 0.25 g. oftitanium isopropoxide. The relative reactivity was 5.4.

EXAMPLE 5 Example 3 was repeated, with the addition of 0.05 g. oftitanium isopropoxide. The relative reactivity was 2.2.

EXAMPLE 6 Example 3 was repeated, with addition of 0.125 g. of zirconiumisopropoxide. The relative reactivity was 3.7.

EXAMPLE 7 Example 3 was repeated. with the addition of 0.036 g. ofzirconium hydride. The reaction proceeded too slowly to measure arelative reactivity.

7 EXAMPLE 8 Example 3 was repeated, with the addition of 0.072 g. oftitanium hydride. The reaction proceeded too slowly to measure arelative reactivity.

EXAMPLE 9 Example 3 was repeated, with the addition of 0.02 g. offinely-divided titanium powder. The reaction proceeded too slowly tomeasure a relative reactivity.

EXAMPLE 10 Example 3 was repeated, with the addition of 0.12 g. oftitanium dioxide. The reaction proceeded too slowly to measure arelative reactivity. The unsuccessful Examples 9-12 illustrate that itis not merely the choice of the metal component of the catalyst which isimportant and points out the necessity for selecting the catalyst inaccordance with the teachings of this invention.

EXAMPLE 11 Example 1 is repeated using various grades of aluminum withvarious amounts of impurities elements present, with various olefins andwith various R MZ compounds as defined herein. Similar results areobtained showing improved rate with catalyst presence. Particularlysignificant are' experiments with the alkoxides of titanium and withcatalyst concentration of from 0.01 to percent by Weight of catalystbased on the amount of aluminum powder.

It is seen from the foregoing that excellent results are obtained wherethe catalyst species is obtained with the actual total titanium classmaterials in the feed being quite low, e.g. in Example 5, the amount oftitanium relative to aluminum is about 0.14 percent by weight andnumerous experiments show that 0.1 percent and 0.05 percent aregenerally quite satisfactory. These correspond to about 230, 160 and 80parts per million of titanium. Holding the titanium as low as possibleis highly important in maintaining low titanium contamination of productaluminum alkyls because of the adverse catalytic effect of titanium andits compounds in many subsequent reactions of the aluminum alkyls.

What is claimed is:

1. In a process for producing alkyl aluminum compounds from reactantscomprising aluminum and hydrogen and olefin or alkyl aluminum or boththe improvement which comprises:

catalyzing the reaction with from about 0.01 percent to about 5 percentby weight of a compound R MZ where,

M is selected from the group consisting of titanium,

zirconium and niobium and mixtures thereof,

R is hydrocarbon,

x+y is a valence factor for M, wherein x can be zero or positive,

Z is OR wherein R is hydrocarbon similar to R or different and where Zis plural, they can be similar or different.

2. The process of claim 1 wherein the reactants are aluminum, hydrogenand olefin.

3. The process of claim 1 wherein the reactants are aluminum, hydrogenand aluminum alkyl.

4. The process of claim 1 wherein the reactants are aluminum, hydrogen,olefin and aluminum alkyl.

5. The process of claim 1 wherein the compound is R TiZ where,

R is hydrocarbon,

x-l-y is a valence factor for Ti, wherein x can be zero or positive,

Z is OR' wherein R is hydrocarbon, similar to R or different, and whereZ is plural, they can be similar or different.

6. The process of claim 1 wherein the compound is fed as M(OR') where,

M is selected from the group consisting of titanium,

zirconium and niobium, and mixtures thereof,

y is a valence factor for M,

R is similar or different hydrocarbon.

7. The process of claim 1 wherein the compound is fed as THOR), where,

R is similar or different hydrocarbon.

8. The process of claim 1 wherein the catalyst is generated in situ froma compound of the type M(OR) added to the reaction system, where M isselected from the group consisting of titanium,

zirconium and niobium, and mixtures thereof,

y is a valence factor for M,

R is similar or different hydrocarbon.

9. The process of claim 1 wherein the catalyst used is a lowertetraalkoxy titanium compound supplied in the proportion of from about0.025 to about 2.0 weight percent based on the aluminum.

10. The process of claim 1 wherein the catalyst used is tetraisopropoxytitanium supplied in the proportion of from about 0.05 to about 0.5weight percent based on the aluminum.

References Cited UNITED STATES PATENTS 3,207,770 9/1965 Ziegler et a1.

3,104,252 9/1963 Radd et al.

3,262,957 7/1966 Roha et a1.

3,381,024 4/1968 Toyoshima et al.

3,382,269 5/1968 Williams et al.

3,402,190 9/1968 TOyOShima et a1 260448 OSCAR R. VERTIZ, PrimaryExaminer H. M. S. SNEED, Assistant Examiner

